This one is no trouble at all. Place the ramdisk kernel at the root of
your nfs mountpoint, named netbsd. This ramdisk kernel
contains the /dev entries and install tools. The bootloader
should just load this kernel and immediately start the install tools.

This is only slightly more work than the ramdisk kernel. You might find a
diskimage.tgz archive, which will include all of the necessary
files (including kernel, /dev entries, and install tools). Untar this
into your client's nfs mount point. When the client starts, it will
immediately start running the install tools.

If you're running NetBSD on your NFS server (or some other OS which can
mount NetBSD filesystems, such as OpenBSD or FreeBSD), then you can mount
your platform's miniroot-fs via a vnode disk driver and use that
as your client's nfs mount point. This will immediately boot the client
into the install tools. To set this up, you'd run something like:# vnconfig -c /dev/vnd0c /path/to/miniroot-fs# mount -o ro /dev/vnd0c /export/client/root

This one is a little more effort. Bascially, you might find some scripts
called install.md, install.sh, install.sub, and
upgrade.sh. You'll need a minimally netbootable system before
you can run these scripts.

The easiest way to do this is to extract base.tgz,
etc.tgz, and kern.tgz. Then you need to run
cd /dev;./MAKEDEV all. Once you've done these steps,
then you'll just run /install.sh to start the install tools.

Oh well. You'll need to extract base.tgz,
etc.tgz, and kern.tgz. Then you need to run
cd /dev;./MAKEDEV all. Once you've done these steps,
netboot your client. Now, you need to disklabel your hard drive using
disklabel(8).
Be sure to use the -B option or the
installboot(8)
tool to make the drive bootable.

Make sure the miniroot filesystem is available on your client's nfs mount.

Next, you should dump the miniroot to your swap partition:
dd if=/path/to/miniroot-fs of=/dev/sd0b bs=4k
Where sd0b is the device for your drive's swap partition.

Now you boot from that hard drive, specifying in the bootloader to boot
from the miniroot partition.

This one's a little daunting, but still possible. You need to follow the
rest of the directions for installing NetBSD for a diskless client.
The page on your the NFS filesystem will have a link to a page describing
what you need to do to get your client to boot into multi-user mode.
You can skip the last diskless step (Finishing up
your installation), as this won't be a permanent diskless setup.

Once your system is set up and boots into multi-user mode, you can install
NetBSD onto your local hard drive using the standard install scripts (you
can't use the ramdisk kernel, as you need to boot a full NetBSD system
with inetd and telnet running).